This invention relates to a film for rubber bales. In one aspect, it relates to a method for transporting rubber in bulk form. In another aspect it relates to rubber bales covered with a microembossed film. (The term "rubber" means synthetic rubber as defined in ASTM D-1566.)
In the manufacture of synthetic rubber such as butyl rubber, chlorobutyl, EPDM, EPR, etc., raw rubber pieces (referred to as "crumbs") are passed from the reactor though a drying oven, and collected in a compression mold where they are compressed into bales of dimensions generally in the range of 14".times.28".times.8". The bales are then placed in large containers ("bins") sized to receive from 30 to 45 of the bales for storage and transport. At the location of use (e.g. tire manufacturing plant), the bales are withdrawn from the bin and individually processed.
The bales are placed in the bin at elevated temperatures (120.degree. F.-210.degree. F.) which causes bale-to-bale sticking problems, particularly for the bales in the lower part of the bin. The sticking and cold flow of the rubber makes it difficult to remove individual bales from the bin. It is not economically feasible to permit the bales to cool to room temperature before placing them in the bins.
In years past, the bins included two corrugated dividers to provide the bins with three compartments for receiving three bale stacks. The individual bales were coated with talc or other particulate material in an effort to reduce bale-to-bale sticking. The coating process was not only not very successful, its application as a powder created health problems. This lead to the development of a thermoplastic film bale wrap. The bale wrap film is applied by conventional in-line equipment to completely encapsulate the rubber bale after the drying and molding steps but prior to being placed in the bin. The film thus prevents rubber-to-rubber contact and also resists cold flow of the rubber. The present bale wrap films include high pressure, low density homo polyethylene (LDPE) and ethylene vinyl acetate (EVA) copolymer.
Although the LDPE and EVA films were successful in preventing the sticking and the cold flow of the rubber bales, they presented downstream processing problems. Many end use applications can not tolerate the presence of ethylene homo or copolymer thermoplastics such as LDPE and EVE. The rubber bale for these applications must be stripped of the bale wrap film prior to compounding the rubber in mechanical mixers. Release agents such as synthetic waxes are generally added to the film resin to enhance the film pealability. However, existing films even with release agents are difficult to peal away from the rubber. Another problem associated with release agents is their effect on heat seal strength of the bale wrap film. When sufficient release agent is present to insure satisfactory release from the rubber bale, the seal strength suffers, particularly at higher temperatures (above about 250.degree. F.) required to heat seal the film in the bale wrapping operation.